The men were identified as Abdullah El Halabi, 35, Danish citizen of Lebanese origin, and Mohammed Tofik Saleh, 38, Swedish citizen of Iraqi origin.
Both men allegedly joined IS three years ago and received weapons training in Syria, Dogan said.
They illegally travelled back into Turkey 12 days ago, it added.
Armed man holding hospital staff hostage in Istanbul
"The two Daesh (IS) members were planning bloody attacks in Europe," it said.
Police then raided a house where the men were hiding in the southern Adana province near the Syrian border and questioned them for 10 days, it said.
Rescue training: Emergency officers return from Turkey
Swedish intelligence agency SAPO confirmed the arrest of a Swedish national to the Aftonbladet daily.
"We are now concentrating on getting more information about this arrest and finding out what the Turkish investigation has shown," SAPO spokeswoman Nina Odermalm Schei said.
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